The present invention relates to a sheet transport member and in particular to a thermoplastic elastomeric sheet transport member useful in automatic printing machines.
In an electrostaticgraphic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the usual document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive areas. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to a support surface, the photoconductive insulating member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle. Alternatively, the electrostatic latent image may be generated from information electronically stored or generated in digital form which afterwards may be converted to alphanumeric images by image generation, electronics and optics. In such a printer application a beam of light such as a laser beam may be used to selectively discharge the photoconductor. For further details of such apparatus, attention is directed to, for example, U.S. Pat. No. 4,660,963 to Stemmle and U.S. Pat. No. 4,901,117 to Derrick.
Commercial applications of this apparatus have become increasingly complex offering the users a variety of printing and copying options. In addition to being capable of providing printing on one side of a sheet of paper, one of the options of particular interest is the capability of such machines to produce printing on both sides of a sheet of paper, which is referred to as duplex copying or printing. In addition, another capability being provided is that of being capable of providing two-color or highlight color simplex toner images on one side only of the copy or print. In both of these operations, the copy sheet or print sheet passes through the processor more than once. It is conventional in many processors to employ a fusing system wherein the toner image is heated to a temperature of the order of about 400.degree. F. to raise the temperature of the thermoplastic toner material to a level at which it will coalesce and penetrate into the sheet substrate, typically paper fibers. This action is typically performed by a fuser roll which typically has applied to its surface a release agent such as a silicone oil to form an interfacial layer between the surface of the fuser roll and the toner image on the copy or print sheet which splits when the copy or print sheet passes through the fusing nip providing release of the toner from the fuser roll surface. As a result, the copy or print sheet has a small amount of silicone release agent on its surface. This silicone release agent has been found to have an adverse effect on the reliability of transport members such as duplex feed rolls which may subsequently come into contact with the sheet having once passed through the fuser. Typical transport members that experience a difficulty include feed rolls and transport rolls made from isoprene or EPDM, (terpolymer elastomer made from ethylene-propylene diene monomer) for example, wherein after a relatively short period of time of feeding or transporting once fused sheets a layer of silicone oil forms on the surface of the transport or feed roll forming an oil slick making the surface slippery and dramatically reducing the reliability of the feeding or transport mechanism. This is particularly prevalent in friction retard feeders which use a high friction driver material for feeding sheets of paper and a somewhat lower friction retarding material whose function it is to ensure that only a single sheet is fed at a time. This difficulty is minimized by the selection of several silicone elastomeric materials to be used in a friction retard feeder device because the silicone rubber surface absorbs the silicone oil with a very slight swelling at the surface and thereby a softening of the silicone rubber which maintains a higher coefficient of friction altogether in the presence of the silicone oil.
Certain machine geometries or designs may require a feeder to perform both the feeding of fresh paper for simplex reproduction and the feeding of once fused oil contaminated paper for duplex reproduction. We have now found that typical silicone rubbers employed in such an environment become unreliable sheet feeders due to the surface of the feed members becoming contaminated with paper fibers and fillers from the virgin paper. Contaminates such as clay, talc, and starches adhere to the surface of the feeder transport rolls thereby decreasing the reliability of the feeder transporting member. In addition, small paper fibers which have been transferred to the roll of the feeder transport member may act like little roller bearings on the surface of feeder transport member further contributing to the feeding and transporting unreliability. Accordingly there is a need for a feeding and transporting member which is capable of performing both the feeding of fresh paper in a simplex mode of printing and feeding of once fused and oil contaminated paper in a duplex printing operation.